Note: Descriptions are shown in the official language in which they were submitted.
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Description
Method for operating a compressor arrangement, and compressor
arrangement
The invention refers to a method for operating a compressor
arrangement, especially a pipeline compressor station, which
compressor arrangement has a turbine and a compressor which are
in torque-transmitting communication, wherein an electrodynamic
machine is in torque-transmitting communication with the
compressor, wherein the turbine with a specified first turbine
output has an efficiency maximum, wherein in the case of a
compressor output below the first turbine output the
electrodynamic machine is operated as a generator, and in the
case of a compressor output above the first turbine output the
electrodynamic machine is operated as a motor. In addition,
the invention refers to a compressor arrangement for the
operation according to the method according to the invention.
In the course of increasing raw material shortage and in the
shadow of the threatening climate change it becomes the
priority task of energy-converting machines to care for the
scarce resources and to limit the emissions, especially the
emission of climate-affecting gases. Therefore, standing by
not only ethical appeals, so-called COz certificates were
introduced in Europe in reaction to resolutions of the Kyoto
protocol, which increases the ecorlomical interests for a
reduction of the emission of so-called greenhouse-gases. This
motivation increasingly also embraces smaller and more special
units.
A task which is related to the previously described problems is
the distribution of natural gas by means of a network of
pipelines which in i.ts mesh-connected state is particularly
difficult to operate iri the case of simultaneously irregular
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distribution of the consumers. At various positions of the
mesh-connected network, sets of agreements specify in which
pressure range which amount of gas in standard cubic meters has
to be made available over a certain period of time. The gas
requirement at the consumer stations in this case is
fluctuating, however, in such a way that the requirement
frequently borders upon the technical limits and, calling upon
all capacities, has to be unconditionally prevented, in such a
way that pressures fall below contractually permissible limits.
This happens at times, however, despite determined use of so-
called pipeline compressor stations and costly trials by means
of mathematical simulations to allow the gas network to
optimally "breathe" at the right moment. In this case, it
frequently happens that the pipeline compressor stations over a
certain period of time create a pressure difference when
delivering the gas in one direction, and during a subsequent
interval of time deliver the gas in the opposite direction.
Within the scope of technical feasibility, a pipeline
compressor station in this case delivers fluctuating volumetric
flows of 0 - 1.000.000 standard cubic meters per hour in both
directions, wherein the drive of the compressor arrangement has
to endure a fluctuation of the driving power of at least 65% -
105%. The compressors of the compressor arrangements are
regularly driven by means of gas turbines which achieve their
optimum efficiency under full load, that is to say at 100%
nominal output, and in the partial load range or in the case of
overload regularly feature dramatic efficiency losses.
Furthermore, the partial load range is also accompanied by
additionally undesirable emissions and a disproportionally high
curtailment of the service life.
Arrangements and principles of operation of the type referred
to in the introduction are already known from WO 2005/047789A2
and US 5.689.141.
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Startirlg from the previously described difficulties, the
invention has made it its task to create methods
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for operating compressor stations, and to create a compressor
station which even in the case of fluctuating load has both
good effi.ciency and good emission values in all load ranges.
For solving the problem, according to the invention a method
which is referred to in the introduction with the features of
claim 1 is proposed, and a compressor plant with the features
of claim 4 is proposed.
As a result of the variable use according to the invention of
the electrodynamic machine, the turbine, which is preferably
designed as a gas turbine, succeeds in constantly operating
closer to the efficiency maximum in the partial load range or
within the range of an overload than is the case with
conventional plants. The entire plant is preferably constantly
operated very close to the efficiency maximum of the turbine or
gas turbine so that both the fuel consumption and the pollutant
emission are minimal.
Should the maximum of the thermal efficiency and the minimum of
the emission not lie at the same operating point of the turbine
or gas turbine, in this case a for example economically
oriented compromise can determirle the preferred operating
point.
The electrodynamic machine, during operation as a motor, is
supplied from an electricity supply system, to which the power
which is generated during operation as a generator is re-
supplied, preferably via the interposition of a frequency
converter. In this way, on the one hand the operator saves on
fuel for the operation, and on the other hand saves on
expenditure for emissions licenses. Furthermore, possibly when
utilizing the non-optimum operating ranges of the turbine, this
arrangement can cope with higher peak loads on account of the
switching-in capability of the electrodynamic machine as a
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motor. A gas turbine, which for example can be operated
between 4 and 8 MW, in combination with an
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electrodynamic machine according to the invention which has 4
MW output, can operate a compressor with an output of between 0
and 12 MW of driving power. If in this case the turbine is
operated only with arl optimum efficiency of for example 7 MW,
the latitude is still between 3 MW and 11 MW of driving power.
In the case of a reversible delivery direction of the
compressor arrangement, even in the case of high fluctuations
with regard to the delivery pressure and the volumetric flow,
exceedingly high efficiencies are achieved with the plant
according to the invention.
The concept according to the invention is suitable both for
compressor arrangements which are operated at constant speed
and for example with an inlet guide vane assembly of the
compressor, and for compressor arrangements with variable
speed, wherein when connecting the electrodynamic machine to
the electric power supply network a frequency converter is
regularly to be provided.
The turbine, especially in the case of a gas turbine, can
advantageously also be brought up to a corresponding speed by
means of the electrodynamic machine for starting, which makes a
separate starter motor for the turbine superfluous.
So undesirable delays do not occur within the scope of
maintenance operations on the compressor, this is preferably
designed in a barrel-type construction and is not provided with
a continuous shaft so that the electrodynamic machine can be
attached orily on one side of the compressor. The
electrodynamic machine in this case is preferably equipped with
a continuous shaft so that either the turbine is connected
directly to the free end, or a torque-transmitting operational
arrangement is preferably coupled to a free end of the
independent turbine shaft. `This second shaft arrangement has
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particular advantages with regard to the use of standard
modules and brings along an expedient shaft dynamic.
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In conjunction with the electrodynamic machine according to the
invention, the rotor dynamic is of particular importance
because a combined shaft train consisting of turbine,
electrodynamic machine and compressor would have a particularly
complex rotor dyriamic, especially with regard to bending
fatigue, on account of the length of the arrangement.
In the following text, a special exemplary embodiment is
described with reference to drawings for clarification. This
description has only exemplary qualities because within the
spirit of the invention further embodiment possibilities also
arise for the person skilled in the art in addition to those
described in detail here. In the drawing:
Figure 1 shows a schematic view of a gas distribution
network,
Figure 2 shows a schematic view of a compressor
arrangement according to the invention which is
operated by means of the method according to the
invention.
Fig. 1 shows a gas distribution network 1 which extends over a
specified territory 2 and has various interfaces 3 to adjacent
regions. At the interfaces, standard volumetric flows U, V, W,
X, Y, Z flow into or out of the gas distribution network 1 of
the territory 2 at specified pressure levels in each case. The
pressure level can lie for example between 50 and 100 bar. In
the case of the gas distribution network 1 it is a mesh-
connected network with a plurality of junction points 9.
Supplier tappings 5, at which gas of a specified individual
pressure pl - plO is tapped from the gas distribution network
1, are located at various sites. At the same time it is
possible that storage feeds into the network take place. The
pressure pl - plO can fluctuate within contractually stipulated
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1.imits which in most cases are stipulated between 50 and 100
bar. At various points in the gas distribution network 1 a
pipeline compressor station PCO or
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compressor arrangement COAN is arranged in each case, wherein
only a single one is exemplarily drawn in Figure 1. The task
of the pipeline compressor station PCO, which corresponds to
the compressor arrangement COAN accordi_ng to the invention, is
to ensure the various standard volumetric flows and pressures
at the supplier tappings 5. The tappings in this case,
especially when seasonally correlated, can fluctuate greatly,
just as the standard volumetric flows U, V, W, X, Y, Z at the
interfaces 3 of the gas distribution network 1 so that only
operating situations which are difficult to predict result for
the pipeline compressor station PCO. Both the pressures pl -
plO and the standard volumetric flows U, V, W, X, Y, Z are
subjected to correspondingly large fluctuations, for example
fluctuations of between 0 and 1.000.000 cubic meters per hour
even when reversing the delivery direction.
Fig. 2 shows a schematic view of the pipeline compressor
station PCO or of a compressor arrangement COAN according to
the invention from Figure 1 in detail, which is operated by
means of the method according to the invention. The compressor
arrangement COAN according to the invention of the exemplary
embodiment essentially comprises a gas turbine GT with a
compressor COGT and a turbine GTGT, an electrodynamic machine
GeMo according to the invention, and a compressor Co. The
compressor Co is located with the electrodynamic machine GeMo
on a first shaft train SH1. The turbine compressor COGT
together with the turbine GTGT of the gas turbine is located on
a second shaft train SH2 which is in a torque-transmitting
communication, in the form of a transmission TR1, with the
first shaft train SH1. The compressor Co is designed in a
barrel-type of construction so that no provision is made for a
continuous shaft as part of the first shaft train SH1 of the
compressor Co. The side of the compressor casing CoCs from
which no end of the shaft train SH1 emerges can be opened for
maintenance operations so that for example a rotor wheel Rot,
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which is not shown in detail, can be exchanged with only little
expenditure of time.
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The electrodynamic machine GeMo, with a shaft SHGeMo which
continues through a casing, is designed as a component part of
the first shaft train SH1 so that the compressor Co is arranged
on a first end of the shaft SI of the electrodynamic machine
GeMo, and the transmission TR1 is arranged on a second end of
the shaft. The electrodynamic machine GeMo is in electrically
conducting communication with a frequency converter CONV so
that electrical energy with the network frequency of 50 Hz,
which is generated by the electrodynamic machine GeMo at
different rotational frequencies, can be supplied to a
connected electric network ELN. In addition, the frequency
converter CONV serves for speed control of the compressor drive
by means of the electrodynamic machine GeMo.
The compressor Co is connected to the gas distribution network
1 and enables the delivery of volumetric flows (standard
volumetric flows U, V, W, X, Y, Z) according to requirement in
one direction or in the opposite direction of a pipeline PL of
the gas distribution network 1. This possibility is opened up
by means of an arrangement CIR of gas lines PEP and valves VAV.
Depending upon the opening of specific valves VAV, this
arrangement CONV, which also comprises a piping arrangement
which is generally referred to as a"braces connection",
enables a delivery of gas by means of the unmodified compressor
Co in the one direction or in the opposite direction of the
pipeline PL. These two different possibilities are shown in
Figure 2 with dash-dot lines or dashed lines.
The method according to the invention for operating the
pipeline compressor station PCO or the compressor arrangement
COAN makes provision for the gas turbine GT with a specified
output P to have a maximum of the efficiency rl, as is indicated
by means of the sketched diagram in Figure 2. The fluctuating
load demands on the compressor Co, as is indicated in Figure 2
by means of the diagram which shows the volumetric flow V over
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the time T, mean in the case of conventional plants that the
gas turbine GT over long periods of time is to be operated
within the ranges of only moderate efficiency r~. According to
the method accordirlg to the invention for operating the
compressor arrangement COAN, the electrodynamic machine
compensates the load peaks and valleys of the compressor Co so
that the gas turbine is constantly operated closer within the
range of the maximum efficiency GT, that is to say closer to
the efficiency optimum. In this case, it is provided that the
electrodynamic machine GeMo, in the case of a load demand from
the compressor Co which is lower than the first output PI at
which the gas turbine has the efficiency maximum ql, is
operated as a generator, and if the compressor Co has an output
demand which is higher than the first output P1, the
electrodynamic machine is operated as a motor. For this
purpose, a control system CR is provided, which controls the
electrodynamic machine according to the operating situation.
The electric power which is generated during the generator
operation of the electrodynamic machine GeMo is brought to the
network frequency by means of the frequency converter CONV and
supplied to the electric network ELN.
